1. Technical Field
The present invention relates to an optical device that creates optical images in response to image signals and a projector equipped with the optical device.
2. Related Art
A projector that project images onto a screen on the wall require high luminance for bright images and a reasonable price with small-size. High luminance is for users' demand for clear images even at the bright surroundings and small-size with a reasonable price is for the demand from home. Further, as image sources from ground wave digital broadcasting have recently increased in resolution, high resolution is required for projector.
As for such projector, the projector that used three LCD have been on the market. Projector is each equipped with a built-in optical device for creating optical images in response to image signals and the image quality of the projectors depends on the performance of the optical device.
An optical device for the projector that used three LCD is configured by three light modulators of transmissive liquid crystal panels for each primary color of light components, i.e. red R, green G, and blue B, and a combining optical unit that combines converted-color light components to produce each color image out of corresponding light modulators and then irradiates the combined-modulated light components with full color.
FIG. 5 is a perspective assembly view of an optical device in the related art.
An optical device for projector that used three LCD is disclosed in JP-A-2005-234124. FIG. 5 shows the attachment structure of only the light modulator 236R for a R-light component to simplify explanation.
An optical device 210 includes a combining optical unit 220 that is formed of a cubic glass prism and light modulators 236R, 236G, 236B (236G and 236B are not shown) that are mounted at incident surfaces Sr, Sg, Sb of three sides, except a irradiating surface So, of the combining optical unit. The light modulator 236R operates as a transmissive liquid crystal panel including a liquid crystal light valve 234R, a irradiating polarizing plate 232R, and an incident polarizing plate (not shown), and the incident polarizing plate is not shown in the figure.
A transparent reinforcing plate 231 with the irradiating polarizing plate 232R bonded and the liquid crystal light valve 234R are supported by a metallic fixing frame 230 fixedly bonded to the incident surface Sr and fixed to the combining optical unit 220 by an intermediate frame 233 and fixing pins 235.
The fixing frame 230 has a U-shape when seen from above and the bottom of the U-shape is bonded to the incident surface Sr. Further, a rectangular opening is formed through the bottom to allow a modulated R-light component out of the light modulator 236R to pass through the fixing frame 230 and the frame-shaped periphery of the opening is bonded to the incident surface Sr as the bonding area.
The light modulators on the incident surfaces Sr, Sg, Sb of the combining optical unit 220 irradiate modulated R-light component, G-light component, and B-light component, respectively. The modulated light components that have entered inside the combining optical unit 220 are reflected from and combined by dielectric multilayer films fa, fb in the combining optical unit 220 formed into an assembly of four prisms and then irradiated as a combined-modulated light component to produce a full color image through the irradiating surface So.
However, in the optical device 210, since the fixing frames 230 are bonded to the incident surfaces Sr, Sg, Sb of the combining optical unit 220, an area for bonding the fixing frame is needed for each incident surface. Accordingly, the combining optical unit 220 was large in size. The cost for the combining optical unit 220 is proportional to the size, so that the cost increases with increase in size.
Further, the color light components entering the optical device 210 have high luminous flux density due to the demand for high luminance, so that the optical device 210 requires cooling for discharging heat from light modulation loss. In particular, it has a problem that how to cool the irradiating polarizing plates that are difficult to cool because they are adjacent to the light optical device 220. However, the periphery of the reinforcing plate 231 with the irradiating polarizing plate 232R bonded is supported by the fixing frame 230 with heat conductive, but most planes, other than the periphery, are in contact with air at the front and rear surfaces and not directly contact with the combining optical unit 220 with high heat discharge efficiency, so that it was difficult to sufficiently cool the irradiating polarizing plates.
As described above, the optical device 210 had problems that it was difficult to decrease the size and the cost and sufficiently cool the irradiating polarizing plates 232.
FIG. 6 is a perspective assembly view of another optical device in the related art.
An optical device 250 designed to overcome the problems accompanying the optical device 210 is disclosed in JP-A-2002-139795. FIG. 6 also shows only the attachment structure of a light modulator 236R for a R-light component and incident polarizing plates are not shown. Further, the same parts as those in FIG. 5 are represented by the same reference numerals.
According to the optical device 250, a supporting substrate 270 formed of a transparent plate with a irradiating polarization plate 232R bonded in advance is fixedly bonded to the incident surface Sr of a combining optical unit 260. Made of a high heat conductive material such as crystal or sapphire, the supporting substrate 270 is larger than the height of the combining optical unit 260.
A fixing frame 272 having pins for fitting at four corners is fixedly bonded to the supporting substrate 270 and a liquid crystal light valve 234R is fixed by the four pins on the fixing frame.
The fixing frame 272 is bonded to the supporting substrate 270 at the portions protruding up and down beyond the combining optical unit 260 as a major boding area. Therefore, it is possible to decrease the combining optical unit 270 as much as the boding area, so that the size and cost of the combining optical unit 260 are reduced. Further, the cooling efficiency for the irradiating polarizing plate 232R is improved from a structure that the irradiating polarizing plate 232R is in close contact with the supporting substrate 270 with high heat conductivity and they are integrally formed with the combining optical unit 260 with high heat discharge efficiency.
Further, in assembling the optical devices 210, 250, each light modulator for corresponding incident surfaces Sr, Sg, Sb of the combining optical units 220, 260 should be precisely adjusted in position to combine each modulated color light component with corresponding pixels (hereinafter, referred to as alignment).
However, in the optical device 210 in the related art, since the light modulators are supported by the metallic frames 230 bonded to the incident surfaces Sr, Sg, Sb, pixel displacements might be caused by changes in temperature. The pixel displacement appears when the coefficient of thermal expansions of the combining optical unit 220 made from mainly glass and the metallic frames 230 are different, or when the facial dimensional changes due to changes in temperature appear in the alignment direction for the light modulator 236R. In detail, when the dimension changes, relative displacements appear in the light modulator 236R aligned with respect to the combining optical unit 220 and pixel displacements correspondingly appear. Further, as it is required for the projectors to be small-sized and have high resolution for image sources, the pitches between pixels narrow in the light modulator. Accordingly, even though the changes in dimension are the same, the ratio of pixel displacement increases.
Further, for the optical device 250 as well, since the coefficient of thermal expansion is different between the combining optical unit 220 of glass and the supporting substrate 270 of crystal or sapphire and the supporting substrate 270 is bonded to the incident surface Sr of the combining optical unit 260, pixel displacement due to changes in temperature might be caused.
As described above, optical devices in the related art have a problem in that pixel displacements may be caused by changes in temperature.
In order to overcome the above problems, an advantage of the invention is to provide an optical device that reduces pixel displacements with simple configuration and a projector equipped with the optical device.